Polymer-based electroluminescent devices (PLEDs) have the potential for providing inexpensive alternatives to semiconductor-based LEDs. PLEDs may be fabricated by coating the appropriate surfaces with an organic polymer, and hence, do not require the use of high cost fabrication systems such as those utilized in the fabrication of semiconductor devices. A simple PLED may be constructed from an electroluminescent layer sandwiched between an electron injection electrode and a hole injection electrode. More complicated devices utilize electron and hole transport layers between the above mentioned electrodes and the electroluminescent layer.
In spite of the lower construction costs inherent in PLEDs, multicolor displays based on such devices are still quite costly to fabricate. To construct a multicolor display, a patterned deposition of each of a plurality of electroluminescent compounds must be performed. In prior art fabrication systems, a series of masking operations is required to protect the areas that are not to receive a particular electroluminescent compound. The electroluminescent compound is then deposited using vapor deposition, dipping, or spin casting. The mask is then removed and the next mask constructed using conventional photo-resist techniques. Each masking operation increases the fabrication costs and reduces the device yield. Hence, it is advantageous to avoid steps that require masking.
The range of colors that may be generated by a display depends on the range of intensities that can be generated by each color of PLED. In conventional multicolor displays, each pixel of the picture is generated by controlling the intensity of each of three sub-pixels, one for each of the primary colors. If a particular electroluminescent dye has a limited dynamic range, the resulting pixel of the image will be limited to less than the full range of colors.
Finally, it is difficult to generate inexpensive displays that display a single fixed image of the type used in point of sale advertising. If a conventional display is used, the image must be stored in a memory external to the display and the display operated in a mode in which the stored image is continuously scanned into the display. The pixels of the display must be individually addressable which further increases the cost of the display.
Broadly, it is the object of the present invention to provide an improved display based on PLEDs.
It is a further object of the present invention to provide a display that may be more inexpensively fabricated than prior art displays.
It is a still further object of the present invention to provide an improved method for fabricating PLED displays.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.